In a typical cellular radio communication system (wireless communication system), an area is divided geographically into a number of cell sites, each defined by a radio frequency (RF) radiation pattern from a respective antenna or antenna system. The antennas in the cells are in turn coupled to one or another form of controller, which is then coupled to a telecommunications switch or gateway, such as a mobile switching center (MSC) and/or a packet data serving node (PDSN) for instance. These (and possibly other) elements function collectively to form a Radio Access Network (RAN) of the wireless communication system. The switch or gateway may then be coupled with a transport network, such as the PSTN or a packet-switched network (e.g., the Internet).
Depending on the specific underlying technologies and architecture of a given wireless communication system, the RAN elements may take different forms. In a code division multiple access (CDMA) system configured to operate according IS-2000 and IS-856 standards, for example, the antenna system is referred to as a base transceiver system (BTS), and is usually under the control of a base station controller (BSC). In a universal mobile telecommunications system (UMTS) configured to operate according to Long Term Evolution (LTE) standards, the antenna system is usually referred to as an eNodeB, and the entity that typically coordinates functionality between multiple eNodeBs is usually referred to as a mobility management entity (MME). Other architectures and operational configurations of a RAN are possible as well.
A subscriber (or user) in a service provider's wireless communication system accesses the system for communication services via a communication device, such as a cellular telephone, “smart” phone, pager, or appropriately equipped portable computer, for instance. In a CDMA system the communication device is referred to as an access terminal (also referred to herein by “AT”); in an LTE system the communication device is referred to as user equipment (also referred to herein by “UE”). When an AT or UE is positioned in a cell, it communicates via an RF air interface with the BTS or eNodeB antenna of the cell. Consequently, a communication path or “channel” is established between the AT or UE and the transport network, via the air interface, the BTS or eNodeB, the BSC or MME, and the switch or gateway.
As the demand for wireless communications has grown, the volume of call traffic in most cell sites has correspondingly increased. To help manage the call traffic, most cells in a wireless network are usually further divided geographically into a number of sectors, each defined respectively by radiation patterns from directional antenna components of the respective BTS or eNodeB, or by respective antennas. These sectors can be referred to as “physical sectors,” since they are physical areas of a cell site. Therefore, at any given instant, an AT or UE in a wireless network will typically be positioned in a given physical sector and will be able to communicate with the transport network via the BTS or eNodeB serving that physical sector.
The functional combination of a BTS of a cell or sector with a BSC, or of an eNodeB (possibly in combination with an MME), is commonly referred to as a “base station.” The actual physical configuration of a base station can range from an integrated BTS-BSC or eNodeB unit to a distributed deployment of multiple BTSs under a single BSC, or multiple eNodeBs under a single MME. Regardless of whether it is configured to support one cell, multiple cells, or multiple sectors, a base station is typically deployed to provide coverage over a geographical area on a scale of a few to several square miles and for tens to hundreds to several thousands (or more) of subscribers at any one time.